What triggers seizures in neurocysticercosis? A MRI-based study in pigfarming community from a district of North India
Amit Prasad a, Rakesh K. Gupta b, Sunil Pradhan c, Mukesh Tripathi d,Chandra M. Pandey e, Kashi N. Prasad a,⁎
a Department of Microbiology, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Lucknow-226014, Indiab Department of Radiology, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Lucknow, Indiac Department of Neurology, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Lucknow, Indiad Department of Anesthesia, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Lucknow, Indiae Department of Biostatistics, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Lucknow, India
Received 13 June 2007; received in revised form 25 November 2007; accepted 1 December 2007Available online 8 December 2007
Keywords: Neurocysticercosis (NCC); Brain; Magnetic resonance imaging; Seizures; Taenia solium
1. Introduction
Neurocysticercosis (NCC), caused by larval stage of thetapeworm Taenia solium, is the most common parasitic infectionof the central nervous system (CNS) in humans in South Africa,Eastern Europe, South America and South East Asia; its incidencevaries from 2.5–8.5 per thousand individuals [1–4]. NCC isbecoming a serious problem with its worldwide distribution [5].ParenchymalNCCpresentswith seizures and headache in 50–80%cases [6]. Thus in endemic areas, it is considered in the differential
diagnosis for a new-onset seizure. Besides these two commonsymptoms, it also produces focal neurological deficit, chronicmeningitis, and hydrocephalus [7]. The symptoms and signs ofNCC are non-specific and depend upon the number, topology andstage of the cyst as well as the host immune response to the parasitein the brain [8,9]. Seizures may be single, clustered or recurrent;and either focal with or without secondary generalization ormay begeneralized at the onset. According to present understanding,viable cysts with little or no enhancement or edema on imaging areusually not associated with symptoms [1]. Acute seizures are morefrequent with the transitional form owing to the pericysticinflammatory host immune response [10]. In most patients,symptoms occur years after the initial invasion of the nervoussystem by the parasite, either by inflammation around the parasite,mass effect, or residual perilesional scarring [10–12]. The single
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calcified lesion is considered to be one of the causes of chronicepilepsy, as the calcified cysts with persistence of scolexmay act assource of antigen that provokes inflammatory reaction [12–14].Seizures may also be due to infarcts caused by perivascularinflammation of degenerating subarachnoid cysts in close contactwith blood vessels.
The clinical course of symptomatic and asymptomatic NCCis poorly understood. None of the published studies has followedthe asymptomatic NCC cases for the development of seizure;most of the studies have demonstrated the association of brainimaging findings in patients with seizure [14,15]. Patients withsevere refractory seizures may have only one calcified lesion; onthe other hand there are patients with multiple cysts orcalcifications but no seizures [16,17]. Though seizures arecommon events in patients with NCC in most of the studies, theexact relationship between seizure and NCC is not yet clear [18].
While working in a pig farming rural community todetermine the prevalence of NCC related seizure, we screenedasymptomatic family members of the individuals with NCCrelated seizures in order to detect asymptomatic NCC cases andthe stage of the parasite. The aim of this imaging based studywas to explore the association of different stages of the cysts inasymptomatic and symptomatic individuals.
2. Methods
2.1. Study population and data collection
The data for this study has been taken from a rural survey toassess the magnitude of T. solium taeniasis and systemiccysticercosis of pig farming community in Mohanlalganj block,Lucknow district of Uttar Pradesh, which is the largest state ofIndia. More than 45% populations of this block belong to pigfarming community, and pig to human ratio is 1:2 in the locality.Pork and pork products are accepted as food in this communityand the study area is highly endemic for T. solium taeniasis [19].Patients with epilepsy among the pig farming community wereidentified during a door-to-door survey. A structured question-naire was developed to collect information from all individuals ofhouseholds having patients with epilepsy. Diagnosis of NCC insymptomatic (patients with epilepsy) and asymptomatic popula-tions was made based on clinical, imaging (MRI), immunological(EITB) and epidemiological criteria [20,21]. Seizures in patientswere classified according to the guidelines of InternationalLeagueAgainst Epilepsy [22]. A total of 60 patients with epilepsyagreed for clinical, immunological and imaging (MRI) evalua-tions. Definitive diagnosis of symptomatic NCC (NCC withepilepsy) was made in 29 of them. A total of 107 asymptomaticfamily members of these 29 NCC related seizure cases volun-teered for NCC evaluations. Asymptomatic cases were defined asindividuals with no evidence/history of seizure, sensory or motorneuro-focal deficit, cranial nerve involvement and psychiatric orbehavioral abnormalities. We selected family members of theindividuals suffering from NCC related seizures, as it was easy toconvince them to volunteer for the study. Asymptomatic caseswere followed up for six months for the development of anysymptoms related to NCC.
The Institute's ethics committee approved the work and allindividuals included in the study consented for enrollment.
2.2. Magnetic resonance imaging (MRI) of brain
With informed consent,MRIwas performed in all these cases ona 1.5 Tesla scanner (Echo-speed plus, General Electric,Milwaukee,USA) using quadrature transmit–receive head coil. The base lineT2 [repetition time (TR)/echo time (TE)/number of excitations(NEX)=4900 ms/85 ms/2)], T1 (TR/TE/NEX=650 ms/9 ms/1)with slice thickness of 5 mm, 0.5 mm interslice gap, 256×256matrix. As a part of the routine protocol gradient echo (GRE)sequence with corrected phase was also performed to detect thecalcification with TE/TR/FA=40 ms/800 ms/20° [15,23]. Post-contrast T1 imaging was also performed after injecting gadodia-mide (Gd-DTPA-BMA, Omniscan, Amersham Health As, Oslo,Norway) intravenously at a dose of 0.1mmol/kg bodyweight.MRIwas evaluated by the radiologist who was blinded to the clinicalstatus of the individuals. The lesions were classified into differentstages (vesicular, colloidal/degenerative, calcified and more thanone stage) as described earlier [23]. We also quantified the volumeof edema in cases having colloidal/degenerative cyst from T2-weighted image using NIH image J software program.
2.3. Enzyme electroimmune transfer blot (EITB)
At the time of MRI, blood was collected with consent of theindividual for EITB as described earlier [24], and the samplewas considered positive if one or more bands of b50 kd weredetected.
2.4. Statistical methods
Overall association between different stages was determinedby Chi square test, while proportion of stages of cysts, number ofcysts, location of cysts in brain and symptoms were analyzed byz-test. The difference between volumes of edema was comparedby independent t-test. Analysis was done using SPSS statisticalsoftware, version 14.0 (SPSS Inc., Chicago, IL, USA).
3. Results
3.1. MRI-based studies on cerebral lesions
A total of 60 patients with epilepsy consented to undergoclinical, immunological (EITB) and brain MRI studies. On MRIstudy, 29 (48.3%) of them had cystic lesions in brain and fulfilledthe definitive/probable diagnostic criteria of NCC. Among thefamily members of these 29 symptomatic NCC cases, 31/107(29.0%) showed cystic lesions in the brain on neuroimaging andfulfilled the definitive/probable diagnostic criteria of NCC.Higher proportion of patients with epilepsy had NCC than thehousehold members (48.3% vs. 29.0%; P=0.019). Partialseizures with secondary generalization were the most commonfinding (14/29; 48.3%) among NCC positive patients withepilepsy, followed by complex partial seizures 7 cases (24.1%),generalized seizure 5 cases (17.2%) and unclassified seizure 3
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cases (10.3%). Fig. 1a–c show the distribution of symptomaticand asymptomatic NCC cases according to the number, locationand staging of cystic lesions in the brain, respectively. The total
number of cysts identified in symptomatic cases was 62,while inasymptomatic family members it was 47. Occurrence of singlecyst was the most common finding in both symptomatic andasymptomatic groups (44.8% and 64.5%, respectively) (Fig. 1a).In symptomatic group the cysts were most commonly localizedat multiple sites (44.8%) followed by frontal lobe (34.5%), whilein the asymptomatic group frontal lobe (45.2%) was mostcommonly involved followed by multiple sites (25.8%)(Fig. 1b). Cysts at the calcified stage were most common inboth symptomatic and asymptomatic groups, 44.8% and 35.5%,respectively (Fig. 1c).
Significantly higher proportions of asymptomatic familymembers had vesicular cysts in their brain as compared tosymptomatic (epileptic) patients on z-test (22.6% vs. 3.4%;P=0.029). However, no significant association was observedbetween presence or absence of seizures and other stages(colloidal/degenerative, calcified andmore than one stage) of theparasite (P=0.176), location of cyst in the brain (P=0.359) aswell as with the number of cysts present (P=0.301) on Chisquare test. In both groups, single cyst (symptomatic vs.asymptomatic, 44.8% vs. 64.5%) and calcified stage (sympto-matic vs. asymptomatic, 44.8% and 35.5%) were the mostcommon finding. The representative figures of different stagesof cysts among symptomatic and asymptomatic cases are shownin Figs. 2 and 3, respectively. The most interesting observationwas that 5 (16.1%) NCC positive asymptomatic family membershad colloidal/degenerative parasite with rim enhancement and 3(9.7%) with calcified lesions were having perilesional edema onpost-contrast study. There was no significant difference betweenthe volume of edema around the colloidal/degenerative cyst ofsymptomatic and asymptomatic cases (P=0.068).
3.2. EITB studies
All the symptomatic and asymptomatic NCC cases werefound to be positive on immunoblot for one or more bands. Themost commonly identified bands were GP24, GP 21, GP 18 andGP 14 either in isolation or in combinations by both sym-ptomatic as well as asymptomatic cases (Fig. 4). The bandGP24 was present in all the cases included in the study.
4. Discussion
Our results show significantly higher proportion of NCC insymptomatic cases than asymptomatic family members. The
Fig. 1. MRI-based cyst burden and staging in symptomatic (grey bar) andasymptomatic (dotted bar) individuals from pig farming community withneurocysticercosis (NCC). (a) Distribution of cyst burden in symptomatic vs.asymptomatic NCC cases; single cyst (44.8% vs. 64.5%, P=0.126), two cysts(27.6% vs. 16.2%, P=0.282), and multiple cysts (27.6% vs. 19.4%, P=0.451).(b) Distribution of cyst according to location in symptomatic vs. asymptomaticNCC cases; frontal lobe (34.5% vs. 45.2%, P=0.398), temporal lobe (13.8% vs.12.8%, P=0.343), parietal lobe (0 vs. 9.7%, P=0.085), occipital lobe (6.9% vs.6.5%, P=0.944), and multiple locations (44.8% vs. 25.8%, P=0.122).(c) Distribution of MRI-based staging of cysts in symptomatic vs. asymptomaticNCC cases; 1. Vesicular (3.4% vs. 22.6%, P≤0.029), 2. Colloidal/degenerating(24.1% vs. 16.1%, P=0.438), 3. Calcified/healed (44.8% vs. 35.5%, P=0.460),and 4. More than one stage (27.6% vs. 25.8%, P=0.876).
Fig. 2. Axial MR images of five clinically diagnosed symptomatic NCC cases with different stages (arrow) of cyst. T2 and T1 weighted axial images (upper and lowerrows, respectively) at different sections show (a) vesicular cyst with scolex in the right occipital lobe, (b) colloidal/degenerating cyst with scolex and perifocal edema inthe right occipital lobe, (c) healing cyst in the right frontal lobe, (d) late healing cyst in the left frontal lobe and (e) multiple calcified lesions in both cerebralhemispheres showing bloom effect on T2⁎ weighted images consistent with calcified lesions.
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distribution of colloidal/degenerating and calcified stages of thecyst in symptomatic and asymptomatic cases was almostsimilar; however, the vesicular stage of parasite was morefrequently present in asymptomatic cases. The interesting ob-servation of the study was that (i) 5 (16.1%) asymptomatic(seizure free) cases had colloidal cyst with contrast enhance-ment and (ii) 11 (35.5%) had calcified lesions (3 with peri-lesional edema as well). However, White and Khun (1997) havereported a clear-cut association between degenerating orinflammatory cyst and seizure [10]. In recently publishedguideline for diagnosis of NCC, Garcia et al. (2005) haveassociated cysts with edema or ring enhancement with symp-
Fig. 3. Axial MR images of five asymptomatic cases with different stages (arrow) ofdifferent sections show (a) vesicular cyst with scolex in the left occipital lobe, (b) coccipital lobe, (c) cyst in the left occipital lobe, (d) cyst in the right parieto-occipitalweighted images consistent with calcified lesions.
toms, while viable cysts with little or no enhancement or edemaare usually not associated with seizure [21]. Nash et al. (2004)has suggested that calcified cysticercosis is not clinically in-active but a cause of seizures or focal symptoms, as they found apositive correlation between endemic population with increasedproportions of calcification and seizure activity [17]. In ourstudy population the presence of large number of asymptomaticNCC individuals with similar distribution of parasite load andstages of the cyst (except vesicular stage) as in symptomaticcases raises a question as to what triggers seizures in NCC. Thisquestion gains further importance as the asymptomatic NCCgroup had similar proportion of degenerating NCC with edema
cyst. T2 and T1 weighted axial images (upper and lower rows, respectively) atolloidal/degenerating cyst with scolex and perifocal edema in the right parieto-lobe and (e) calcified cyst in right occipital lobe showing bloom effect on T2⁎
Fig. 4. Enzyme electroimmune transfer blot profile of four symptomatic (lanes1–4) and four asymptomatic (lanes 5–8) NCC cases.
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and contrast enhancement, a finding commonly implicated tocause acute seizure in symptomatic NCC patients. Our obser-vations are further supported by a necropsy study on war victimsand road traffic accident deaths that showed a large numbers ofdifferent stages of NCC, in otherwise asymptomatic individuals[25]. A CT based study in Salama, Honduras had revealed thatthe majority (84%) of individuals with active or calcified NCCcompatible lesions were asymptomatic [26]. Similarly in a studyfrom rural Ecuador, 17 (14.4%) out of 118 randomly selectedhealthy volunteers were having the evidence of NCC on CTneuroimaging [27]. The relative contribution of the cyst stage,parasite genotype, host immune status, genetic make up of theindividuals or combination of factors for the development ofseizure needs to be explored.
MRI is the best neuroimaging tool available for the detection ofdegenerating and innocuous cysticerci [28]. However, the literatureon neuroimaging describesMRI as less sensitive to CT for calcifiedlesions andCT is considered to be the best neuroimaging procedurefor patients with suspected calcified NCC lesions [23]. In generalMRI provides better image detection and definition, and its highcontrast resolution allows it to recognize any form of NCC notvisualized on CT. To our knowledge, this is the first study onMRI-based staging of cyst in asymptomatic subjects in communitysetting and comparison of the occurrence of different stages ofcysts, number of cysts and their location in the brain withsymptomatic NCC cases. Earlier a number of studies had reportedthe occurrence of NCC compatible lesions in healthy controls[26,27,29,30], but none had compared them with symptomaticpopulations.We followed up these patients for six months and theyremained asymptomatic. It has been reported that geneticdifferences in cysticerci may affect their infectivity and pathogeni-city, and may also contribute to the severity of the disease [31].However, to resolve these issues, further studies are required.
EITB is claimed to be the most reliable serologic test withreported sensitivity of 98% and specificity of 100% [24]; however,
in a recently published report from south India, authors had foundonly 12 of 46 (26.1%) patients with CT diagnosis of NCC werepositive by EITB [32]. In a study from Honduras, EITB offeredvaluable information if performed in CSF [33]. We found that allsymptomatic NCC patients as well as asymptomatic cases werepositive on EITB for one or more bands. This is a uniqueobservation and the probable reason for this may be that weconducted the study in a highly endemic community with reportedrate of taeniasis 18.6% and epilepsy 5.6% [19]. In anepidemiologic survey on T. solium cysticercosis, Chung et al.(2005) had reported that all individuals with high antibody titer forcyst fluid antigens had multiple bands on immunoblot [34]. Case-control studies in larger sample size are required to evaluate therole of EITB for diagnosis of NCC in highly endemic areas and incommunities at higher risk for infection.
The presence of degenerating NCC in the asymptomaticgroup questions the need of prophylactic treatment with anti-epileptic and anti-parasitic drugs for such individuals. Theoption to follow-up such individuals with imaging and to treatthem only if they become symptomatic needs to be explored.
Our data suggests that a large number of the people harboringdifferent stages of NCC remain asymptomatic. What triggersseizure in some patients and why others with similar stage of theparasite (as seen on MRI) remain symptom free is not clearlyunderstood. Prospective cohort studies involving differentstages of the parasite in a large asymptomatic population witha long-term follow-up and analysis of the host immune status,genetic, hormonal or sex related factors as risk for seizures mayclarify the relation between NCC and epilepsy in future.
Acknowledgements
This work was supported by the grant from the Indian CouncilofMedical Research (File No. 5/3/3/9/2002-ECD-I). Amit Prasadacknowledges the financial assistance from the University GrantCommission, NewDelhi, India.We thankDr. Sandeep Srivastavafor his help in the fieldwork.
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